A compact electrochemical sensor module for pH detection was developed for potential
integration into specialized devices used for live cell or tissue incubation, for
applications in highly parallelized cell culture analysis, by incorporating Organ-on-Chip
devices. This research focuses on the deposition, structural and chemical analysis,
and functional characterization of different titanium-oxide layers with various compositions
as potentially sensitive materials for pH sensing applications. The titanium-oxide
layers were deposited using vacuum sputtering and atomic layer deposition at 100 °C
and 300 °C, respectively. Transmission electron microscopy and X-ray photoelectron
spectroscopy were utilized to determine the specific composition and structure of
different titanium-oxide layers. These TiOx-functionalized electrodes were connected
to the application-specific analog front-end chip of the low-power readout circuit
for precise evaluation. The pH sensitivity of the differently modified electrodes,
employing various TiOx materials, was evaluated using pH calibration solutions ranging
from pH 6 to 8. Among the various deposition solutions, such as sputtering or high-temperature
atomic layer deposition, the TiOx layer deposited using low-temperature atomic layer
deposition proved more suitable for pH sensing applications, with a sensitivity of
54.8–56.7 mV/pH, which closely approximates the Nernstian response.
